Various abbreviations that may appear in the specification and/or in the drawing figures are defined as follows:    3GPP third generation partnership project    UTRAN universal terrestrial radio access network    EUTRAN evolved UTRAN (LTE)    LTE long term evolution    Node B base station    eNB EUTRAN Node B (evolved Node B)    UE user equipment    UL uplink (UE towards eNB)    DL downlink (eNB towards UE)    EPC evolved packet core    MME mobility management entity    S-GW serving gateway    MM mobility management    PHY physical    RLC radio link control    RRC radio resource control    RRM radio resource management    MAC medium access control    PDCP packet data convergence protocol    O&M operations and maintenance    BW bandwidth    FDMA frequency division multiple access    OFDMA orthogonal frequency division multiple access    SC-FDMA single carrier, frequency division multiple access    TTI transmission time interval    EDGE enhanced data rates for global evolution    SMPS switched mode power supply
A proposed communication system known as evolved UTRAN (E-UTRAN, also referred to as UTRAN-LTE or as E-UTRA) is currently under development within the 3GPP. The current working assumption is that the DL access technique will be OFDMA, and the UL access technique will be SC-FDMA.
One specification of interest is 3GPP TS 36.300, V8.3.0 (2007-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Access Network (E-UTRAN); Overall description; Stage 2 (Release 8), incorporated by reference herein in its entirety.
FIG. 1 reproduces FIG. 4 of 3GPP TS 36.300, and shows the overall architecture of the E-UTRAN system. The E-UTRAN system includes eNBs, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an EPC, more specifically to a MME (Mobility Management Entity) by means of a S1-MME interface and to a Serving Gateway (S-GW) by means of a S1-U interface. The S1 interface supports a many-to-many relation between MMEs/Serving Gateways and eNBs.
The eNB hosts the following functions:
functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, allocation of resources to UEs in both uplink and downlink (scheduling);
IP header compression and encryption of user data stream;
selection of a MME at UE attachment;
routing of User Plane data towards Serving Gateway;
scheduling and transmission of paging messages (originated from the MME);
scheduling and transmission of broadcast information (originated from the MME or O&M); and
measurement and measurement reporting configuration for mobility and scheduling.
The LTE Layer 1 (PHY) is defined in such a way as to adapt to various spectrum allocations. In general, the PHY layer specification can be found in 3GPP TS 36.213, V8.2.0 (2008-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures (Release 8), and 3GPP TS 36.211, V8.2.0 (2008-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation (Release 8).
Referring specifically to subclause 5.2 of 3GPP TS 36.211, V8.2.0, “Slot structure and physical resources”, in subclause 5.2.1 a resource grid is shown and described. FIG. 5.2.1-1, reproduced herein as FIG. 2A, shows the UL resource grid as currently defined. The transmitted signal in each slot is described by the resource grid of NRBULNSCRB subcarriers and NsymbUL SC-FDMA symbols. The quantity NRBUL depends on the uplink transmission bandwidth configured in the cell and fulfils the relationship:NRBmin, UL≦NRBUL≦NRBmax, UL,where NRBmin, UL=6 and NRBmax, UL=110 is the smallest and largest UL BW, respectively, supported by the current version of the specification. The set of allowed values for NRBUL is given by 3GPP TS 36.104, Evolved Universal Terrestrial Radio Access (E-UTRA); Base Station (BS) radio transmission and reception.
The number of SC-FDMA symbols in a slot depends on the cyclic prefix length configured by higher layers and is given in Table 5.2.3-1, reproduced herein as FIG. 2B.
As is described in subclause 5.2.2, “Resource elements”, each element in the resource grid is referred to as a resource element and is uniquely defined by the index pair (k,l) in a slot where k=0, . . . , NRBULNSCRB−1 and l=0, . . . , NsymbUL−1 are the indices in the frequency domain and the time domain, respectively. Resource element (k,l) corresponds to the complex value ak,l. Quantities ak,l. corresponding to resource elements not used for transmission of a physical channel or a physical signal in a slot are set to zero.
Subclause 5.2.3, “Resource blocks”, defines a physical resource block as NsymbUL consecutive SC-FDMA symbols in the time domain and NSCRB consecutive subcarriers in the frequency domain, where NsymbUL and NSCRB are given by Table 5.2.3-1 (FIG. 2B herein). A physical resource block in the UL thus consists of NsymbUL×NSCRB resource elements, corresponding to one slot in the time domain and 180 kHz in the frequency domain.
Power amplifiers in mobile wireless devices consume a significant amount of the total energy contained in the battery, and their overall efficiency is a key design issue. To achieve good efficiency, polar transmitter architectures are being proposed and used. Typically, a polar transmitter includes a switched mode power supply (SMPS) that provides a time-varying supply voltage to the power amplifier with a bandwidth proportional to the modulation bandwidth of the RF signal.
One exemplary polar-type of transmitter arrangement is described in commonly owned US Patent Application Publication US 2006/0178119 A1, “Variable bandwidth envelope modulator for use with envelope elimination and restoration transmitter architecture and method” by Esko Jarvinen, incorporated by reference herein in its entirety. The envelope elimination and restoration (EER) transmitter architecture may be considered to represent a type of polar transmitter architecture.
The trend in future wireless systems is towards wider bandwidths, for example 20 MHz in LTE and up to (for example) 100 MHz for future extensions. In comparison, the design of a SMPS for use in transmitting a conventional WCDMA signal, having a 5 MHz BW, already presents a significant challenge.
One approach to achieve higher bandwidths for the modulated power amplifier supply voltage is the combination of a switched mode supply with a linear regulator. In this case the switched mode power supply achieves good efficiency at a low bandwidth while the linear regulator is capable of achieving a significantly higher bandwidth, but with a lower efficiency.
Commonly owned U.S. Pat. No. 7,058,373, “Hybrid switched mode/linear power amplifier power supply for use in polar transmitter” by Vlad G. Grigore (incorporated by reference herein in its entirety), discloses a linear regulator placed in parallel with a SMPS. This commonly owned US patent describes a DC-DC converter that has a switch mode part for coupling between a DC source and a load, where the switch mode part provides x amount of output power; and that further has a linear mode part coupled in parallel with the switch mode part between the DC source and the load, where the linear mode part provides y amount of output power. In this commonly owned US patent x is said to be preferably greater than y, and the ratio of x to y may be optimized for particular application constraints. In a further aspect of this commonly owned US patent there is described a radio frequency (RF) transmitter (TX) for coupling to an antenna, where the TX has a polar architecture having an amplitude modulation (AM) path coupled to a power supply of a power amplifier (PA) and a phase modulation (PM) path coupled to an input of the PA. The power supply includes the switch mode part for coupling between a battery and the PA and the linear mode part coupled in parallel with the switch mode part between the battery and the PA.
FIG. 3A herein reproduces FIG. 5, and FIG. 3B reproduces FIG. 13A of commonly owned U.S. Pat. No. 7,058,373.
The hybrid voltage regulator or power supply 30 shown in FIG. 3A combines a switching part 32, that processes preferably the majority of the power with high efficiency but low bandwidth, with a linear part 34 that preferably processes a smaller part of the required power with less efficiency but with high bandwidth. The result is a power supply that has the required bandwidth and efficiency somewhat lower than that of a purely switching power supply, but still significantly higher than that of the purely linear regulator. The resulting hybrid power supply 30 provides an improved output voltage quality to a power amplifier (PA) 6, as the linear part 34 can be used to compensate the output voltage ripple that is normally associated with a purely switching mode power supply. This is a significant benefit, as an excessive amount of output voltage ripple can adversely affect the output spectrum of the PA 6.
In principle the amount of power (x) that is processed by the switching part 32 is greater than the amount of power (y) processed by the linear part 34. This is generally a desirable situation and, in fact, in many embodiments x may be much greater than y. Generally it is desirable to maximize the ratio of x to the total power since the larger is this ratio, the higher is the efficiency. However, the actual ratio that is realized in a given application can be a function of one or more of the following factors and considerations (for example):
(a) the intended application (RF system specifics, such as the spectrum of RF envelope, amplitude of high frequency AC components, etc); and
(b) the implementation, where one may decide to some extent how much power to process with the switching part 32 and how much with the linear part 34. For example, in the EDGE system one can process almost all of the power with the switching part 32 by using a 6-7 MHz switching frequency, or less power by using a slower switching converter operating at, e.g., 1 MHz. One may also in certain situations, e.g., at very low power, disable the switching part 32 and use only the linear part 34, in which case the relationship x>y does not apply at all.
In general the portion of the power x processed by the switching part 32 is preferably greater than the portion of the power y processed by the linear part 34, and also the ratio of x to y is preferably optimized for the constraints imposed by a given application, and possibly also by a particular mode of operation (e.g., in the low power mode mentioned above, where all power may be processed by the linear part 34). A combination may also be considered, such that x is preferably greater than y, and the ratio of x toy also may be optimized for the application constraints.
In practice, the embodiments described in the commonly owned U.S. Pat. No. 7,058,373 may be implemented by taking a portion of the topology of a switching converter (referred to in FIG. 3A as the “switching part”) and paralleling it with a voltage or a current source (referred to in FIG. 3A as the “linear part”).
As one non-limiting example of the numerous embodiments disclosed in commonly owned U.S. Pat. No. 7,058,373, FIG. 3B illustrates the source/sink behavior of a Voltage Controlled Voltage Source (VCVS) 34A, and models the behavior of the power amplifier. More specifically, FIG. 3B shows an embodiment with ideal sources, and where the voltage sources VCVS 34A and 34A′ are uni-directional (one sources current, the other one sinks current), although in other embodiments they may be bidirectional.
Existing wireless systems are typically designed for a fixed bandwidth, or a small number of bandwidth modes. However, future wireless systems, such as the LTE system, may operate with a bandwidth that is essentially continuous over a wide range. A need exists to provide a wireless transmitter that is capable of efficient operation in a wireless system such as the LTE system.